1. Field of the Invention
The present invention relates to a brushless AC generator to be mounted on an automotive vehicle such as a truck, a construction vehicle or a farming vehicle.
2. Description of Related Art
Ambient temperature in which an AC generator is used is becoming high because an engine has been modified to improve exhaust gas quality. Further, electric power required for a vehicle is increasing to secure driving safety and comfort. A brushless AC generator has been used in vehicles such as trucks which are driven in a long distance and construction or farming vehicles which are used in a dusty environment. This is because the brushless AC generator is resistive to dust and has a long lifetime.
Generally, in such an AC generator, no window for introducing cooling air is formed in a housing to protect components from being damaged by foreign particles or water entering into the generator. Electric components such as a rectifier are protected by a sidewall of the housing and are cooled by a outside fan fixed to a rotor shaft. To meet a requirement for increasing an output of the generator, various measures, such as increasing a diameter and a thickness of a stator and decreasing resistance in windings, have been taken. Further, a counter measure has to be taken against a temperature rise due to increase in the generator power.
In the brushless AC generator, it is difficult to increase a diameter of the outside fan to increase its cooling ability because there is a limitation in the diameter of a size in a radial direction. There is also a limitation in increasing the number of blades and its area in the axial direction because a mechanical strength of the blades has to be taken into consideration. It is conceivable to make narrower a gap between cooling fins of a rectifier and a sidewall of the housing to increase cooling efficiency. However, if the gap is made narrow, a possibility of accumulation of foreign particles in the gap increases.
An example of the brushless AC generator disclosed in JP-A-2001-292550 includes cooling windows formed in a rear housing, and cooling air is introduced through the cooling windows into the generator by an outside fan disposed at a pulley side. However, there is a problem that cooling air is not smoothly introduced into the housing because a flow of the cooling air is disturbed or stagnated by a step or a gap between the rear housing and an axial end of a rotor. Further, in the case where such a gap is exposed to the cooling window, water or other liquid may enter the gap thereby causing various troubles.